Deprecate all "virtual" commons

[WilcoFiers]

When we were working on axe-core 3.0 we imagined we'd have different methods for DOM nodes and virtual DOM nodes. The later would be called with methods ending with Virtual. Because of that we ended up with methods like accessibleText and accessibleTextVirtual. We've moved away from this approach more recently. More and more of axe runs exclusively on VirtualNodes. It's faster, safer, lets us normalise more consistently, etc. It's far better. Where DOM nodes are needed we can easily get at them from vNode.actualNode.

So, I would like us to find all xxxVirtual methods, make sure their non-virtual counterpart can accept virtual nodes, then deprecate all those xxVirtual methods, and remove their use from the code base.